1. Field of the Invention
The present invention generally relates to an optical disk device which records and reproduces information to/from a writable optical disk, and more particularly, to a technology for preventing the occurrence of a buffer-underrun during a data-recording.
2. Description of the Related Art
A writable optical disk has a relatively large unit into which to write data due to characteristics of a recording format. Many of conventional optical disk devices do not cause a data-recording to an optical disk to pause. Therefore, unless data is transmitted from a host computer to the optical disk device at a higher transfer rate than a recording speed of the optical disk device to the optical disk, the data-recording comes to be suspended. When the data-recording to the optical disk is suspended, the data-recording fails because the data cannot be written additionally.
This is called a buffer-underrun. As the recording speed to the optical disk becomes higher, the buffer-underrun is more likely to occur, and the resulting failure of the data-recording poses a serious problem for a user, because a CD-R is a write once type, in which a failure of a data-recording means a loss of an optical disk and a loss of the data already written or to be written.
A method has been contrived for preventing such a buffer-underrun: increasing a capacity of a buffer RAM provided in an optical disk device for temporarily storing data from a host computer so as to absorb the change in a data transfer speed from the host computer during a data-recording. However, increasing the capacity of the buffer RAM is not a good measure, because increasing the capacity of the buffer RAM leads to raising a cost of the optical disk device as a whole. Additionally, the buffer RAM cannot deal with all cases related to the differences in a throughput of host computers.
Another method contrived is detecting in advance that a buffer-underrun is near to occur so as to change the data-recording speed to an optical disk. However, this method involves a complicated structure and control, because the data-recording speed needs to be switched during a data-recording to the optical disk.
Thereupon, Japanese Laid-Open Patent Application No. 10-49990 discloses an invention which can prevent a buffer-underrun beforehand regardless of a change in a data transfer speed from a host computer by comprising a means for temporarily stopping a data-recording during the data-recording to an optical disk, and a means for resuming the data-recording from a position at which the data-recording is stopped.
In other words, the Japanese Laid-Open Patent Application No. 10-49990 describes that, when a data-transfer from a host computer cannot keep up with a data-recording to an optical disk, the data-recording operation is temporarily stopped until the data-recording is resumed when a sufficient amount of data to perform a data-recording to the optical disk is secured after the data-transfer is resumed. In this arrangement, a displacement in the joint of the two recordings is made extremely small in terms of positional precision so that the data maintains a continuity by a CIRC demodulation, and an area including the joint can be reproduced without causing a serious problem in terms of data-reproduction. Further, as to a means for forming the above-mentioned precise joint, the invention disclosed in the Japanese Laid-Open Patent Application No. 10-49990 is characterized by comprising a means for accurately detecting an end of data recorded last time when resuming a data-recording, and a means for resuming the data-recording from the end of the data.
Such a recording control as disclosed in the Japanese Laid-Open Patent Application No. 10-49990 involves a possibility that a data-recording operation to an optical disk is frequently stopped and resumed. Normally, data transferred from a host computer is temporarily stored in a buffer RAM, and a predetermined parity, etc. is encoded and added to the data. Thereafter, the data is subjected to processes including an EFM modulation so as to be recorded as recorded data on an optical disk. Currently, in a conventional optical disk device, the capacity of the buffer RAM is approximately from 512 kilobytes (Kbytes) to 2 megabytes (Mbytes).
On the other hand, a recording speed to a CD, for example, is 150 Kbytes at a normal speed, and if a recording speed keeps being increased as it currently is, the recording speed becomes 2.4 Mbytes/sec at a sixteen-fold speed. Therefore, all the data temporarily stored in the buffer RAM is to be recorded on the optical disk in as short a time as approximately 0.8 seconds. Accordingly, unless new data is transmitted from the host computer in this short time and then a predetermined parity, etc. is encoded and added to the data, a buffer-underrun occurs in which the recording operation is temporarily stopped. Even though the capability of a host computer connected to an optical disk device is being improved, a possibility that a data-recording operation is frequently stopped and resumed has to be treated properly in order to guarantee a stable operation in association with any host computer.
However, when performing the above-mentioned control of detecting an ending position of the previous recording and accurately resuming the data-recording from the ending position, under the situation where a data-recording operation is frequently stopped and resumed, a displacement may occur between absolute time information (ATIP absolute time information) and a position of recorded data, and when the displacement actually occurs, the displacement is accumulated. When the accumulated displacement surpasses a certain value, the data-recording operation cannot be resumed. As mentioned above, the amount of data that is transferred from a host computer and can be retained in an optical disk device is equivalent to the capacity of a buffer RAM at most. Therefore, unless another data is transferred from the host computer within a period by the end of recording the data stored in the buffer RAM, the recording operation has to be temporarily stopped.
Further, if a change in revolution of a motor occurs during this period, and if the change cannot be absorbed in a motor revolution control, the ending position of the recording is displaced from the absolute position on the optical disk. Thereafter, upon resuming the recording, the displaced ending position of the previous recording is detected, and the data-recording is resumed from the displaced ending position. Accordingly, the displacement from the absolute position on the optical disk is accumulated. In a control of a recording position for resuming a data-recording as an example, a frame address of the aimed position is first detected by using ATIP absolute time information. Next, the ending position is predicted by switching from information obtained by reproducing data recorded on an optical disk to a sub-code frame synchronizing signal.
In this control of determining a position for resuming a data-recording, when the above-mentioned accumulation of displacement surpasses one sub-code frame, the data-recording may be erroneously resumed from a position before the ending position of the previous recording. That is, an overlap occurs in the above-mentioned joint of the two recordings in some case, and, in other case, recorded information is reproduced while the recorded information keeps the displacement from the absolute position information on the optical disk. In both cases, there is a possibility that data may not be reproduced accurately. The seriousness of this problem depends on the number of times a data-recording operation is temporarily stopped and resumed which affects the accumulation of displacement, and also depends on a length of a period from a resumption of the data-recording operation until a stop thereof which affects the time to be taken for a motor revolution control to transit from an unstable state to a stable state. In other words, the above-mentioned possibility becomes greater as the capacity of the buffer RAM becomes smaller, and as the recording speed to the optical disk becomes higher.
It is a general object of the present invention to provide an improved and useful optical disk device in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide an optical disk device which can provide a stable and optimal recording control by, upon resuming a data-recording to an optical disk device, detecting a displacement between the phase of an EFM frame sync signal obtained by reproducing data recorded last time and the phase of a sector synchronizing signal generated by a data-writing reference clock signal generating unit so as to be used to obtain a data-writing timing for recording data to the optical disk device.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention an optical disk device recording information on a recordable optical disk including address information indicating a position of a part of the optical disk having not recorded any data yet, and reproducing information from the optical disk, the device comprising:
a reference clock signal generating unit generating a data-writing reference clock signal used to obtain a data-writing timing upon recording data to the optical disk;
a synchronizing signal generating unit generating a predetermined sector synchronizing signal from the data-writing reference clock signal;
a data demodulating unit reading address information indicating a position on the optical disk from data recorded on the optical disk so as to demodulate the address information into a predetermined synchronizing signal;
a displacement detecting unit detecting a displacement between a phase of the sector synchronizing signal and a phase of the synchronizing signal; and
a data-writing control unit controlling a data-writing upon performing an additional recording to the optical disk by controlling a revolution of the optical disk dynamically according to the displacement.
According to the present invention, an erroneous recording operation can be prevented beforehand. Specifically, a loss of an optical disk and a loss of data already written can be restricted to the minimum when a data-recording fails, and a displacement from an absolute position on the optical disk can be immediately corrected. Therefore, a data-recording operation to the optical disk can be frequently stopped and resumed. Consequently, this can reduce the memory capacity of a buffer memory used in data-recording, realizing an inexpensive, efficient and accurate recording control that can greatly reduce the cost of the optical disk device.
Additionally, in the optical disk device according to the present invention, the data-writing control unit may increase a servo response dynamically to a motor revolving the optical disk, when the displacement surpasses a predetermined value.
According to the present invention, when information is recorded at a position displaced from the absolute position on the optical disk, the displacement can be immediately corrected in the next recording so as to prevent the accumulation of the displacement.
Additionally, in the optical disk device according to the present invention, the data-writing control unit may increase a servo response dynamically to a motor revolving the optical disk, when the displacement surpasses the displacement detected last time by the displacement detecting unit.
According to the present invention, an accumulation of relative displacement from the last recording control can be detected, realizing an efficient, accurate and optimal recording control that can immediately correct the displacement from the absolute position on the optical disk.
Additionally, in the optical disk device according to the present invention, the data-writing control unit may decrease the increased servo response back to a previous degree thereof, when the displacement becomes lower than a predetermined reference value.
According to the present invention, an efficient and accurate recording control to the optical disk can be realized.
Additionally, in the optical disk device according to the present invention, the data-writing control unit may decrease the increased servo response back to a previous degree thereof, when a predetermined period has elapsed since the data-writing control unit increases the servo response.
Additionally, in the optical disk device according to the present invention, the data-writing control unit may decrease the increased servo response back to the previous degree thereof, when a predetermined amount of data has been recorded to the optical disk since the data-writing control unit increases the servo response.
According to the present invention, the servo response can be increased only when necessary, and a period during which the servo response is increased can be limited. This can avoid following noises and erroneous detection of address information indicating a position of a part of the optical disk having not recorded any data yet, which may otherwise result in an unstable motor revolution control, when increasing the servo response in a servo circuit; thus, a stable and optimal recording control can be realized.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention an optical disk device recording information on a recordable optical disk including address information indicating a position of a part of the optical disk having not recorded any data yet, and reproducing information from the optical disk, the device comprising:
a reference clock signal generating unit generating a data-writing reference clock signal used to obtain a data-writing timing upon recording data to the optical disk;
a synchronizing signal generating unit generating a predetermined sector synchronizing signal from the data-writing reference clock signal;
a data demodulating unit reading address information indicating a position on the optical disk from data recorded on the optical disk so as to demodulate the address information into a predetermined synchronizing signal;
a displacement detecting unit detecting a displacement between a phase of the sector synchronizing signal and a phase of the synchronizing signal; and
a data-writing control unit controlling a data-writing upon performing an additional recording to the optical disk by controlling a speed of writing data to the optical disk according to the displacement.
According to the present invention, a period during which to deal with one set of data transferred from outside can be lengthened, i.e., a period from the start of a recording to the end thereof can be lengthened. This lengthened period can increase the probability of absorbing (adjusting and stabilizing) the displacement so as to prevent the occurrence of a displacement beforehand. Therefore, a data-recording operation to the optical disk can be frequently stopped and resumed. Consequently, this can reduce the memory capacity of a buffer memory used in data-recording, realizing an inexpensive, efficient and accurate recording control that can greatly reduce the cost of the optical disk device.
Additionally, in the optical disk device according to the present invention, the data-writing control unit may cause the displacement detecting unit to perform the detecting again after decreasing the speed, when the displacement surpasses a predetermined value.
According to the present invention, a period from the start of a recording to the end thereof can be lengthened so as to increase the probability of absorbing the displacement, preventing the occurrence of a displacement beforehand more surely.
Additionally, in the optical disk device according to the present invention, the data-writing control unit may cause the displacement detecting unit to perform the detecting again after decreasing the speed, when the displacement surpasses the displacement detected last time by the displacement detecting unit.
According to the present invention, not only an accumulation of relative displacement from the previous recording control can be prevented, but also a period from the start of a recording to the end thereof can be lengthened so as to increase the probability of absorbing the displacement, preventing the occurrence of a displacement beforehand more surely.
Additionally, in the optical disk device according to the present invention, the data-writing control unit may start the additional recording to the optical disk, when the displacement becomes lower than a predetermined reference value.
According to the present invention, an efficient and accurate recording control to the optical disk can be realized.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.